A society is, both for judicial and fiscal reasons, interested in safeguarding that a citizen while filling propellants into a motor vehicle may receive the correct amount in accordance with the desired or ordered amount.
Earlier types of propellant pumps have been known in which the propellant was pumped by hand from a subterranean storage tank into one or more measuring glasses which each might have contained f. inst. five liters, whereafter the propellant was poured via an adjustable valve through a hose and a filling nozzle down into the tank of the vehicle. It was hereby possible for the citizen or for an inspector appointed for the task to control the correct amount of propellant, as the measuring glass was provided with indicating marks so that the volume might easily be controlled.
However, these types of propellant pumps were slow in operation and the manual pumping demanded a great deal of working power, and the applicability of the propellant pumps therefore declined concurrently with the rising employment of motor vehicles.
Modern propellant pumps therefore are motor driven and are provided with pumps and measuring means which show the amount of propellant delivered.
However, measuring means of this kind may change in accuracy, f. inst. because of wear or impurities, and a citizen normally has no possibility of controlling the amount of propellant delivered, as this is pumped directly into the tank of the vehicle. The possibility available to a citizen to control the amount of propellant delivered would be for he or she to bring along a volume calibrated container, a so called standard, which would be filled up to a certain graduation mark, whereafter the contents of the container would be poured into the tank, f. inst. by lifting the container and pouring the contents through a funnel and a hose.
Considering that a modern private vehicle has a tank of a volume of 40 liters or more, and that a lorry often may have a tank of several hundred liters, such a control would be Utopian to accomplish for the ordinary citizen because the propellant pump would be blocked for a considerable period.
On the other hand this kind of control has been available for an authorized control of petrol pumps, but it cannot live up to the latest requirements on efficiency, environmental care and fire resistance.
It should be remembered that in the authorized control the measured amount of propellant is not bought, so that the propellant collected in the standard is still the property of the owner of the tank, and that the amount of propellant contained in the standard has to be returned to the storage tank of the petrol station through a filling pipe which for reasons of fire prevention is situated at a considerable distance from the propellant pump. The storage tank is normally for the same reasons situated underground and tank stations are provided with several propellant pumps which all have to be controlled.
To achieve the necessary guarantee of a correct verification or calibration of the individual liquid meter in the propellant pump the control of the liquid pump has to be effected by means of several consecutive fillings and emptyings of the standards.
Furthermore the propellant pumps deliver petrol in an amount of typically 60 liters per minute through filling nozzles which are provided with means for automatical stopping of the pumping if a tank is filled or the propellant during the filling "kicks back", and the calibration of the measuring means of the propellant pump presumes a constant flow from the activation of the filling nozzle to the termination of a delivering process. When the propellant leaves the filling nozzle it is mixed with a great deal of air which in connection with the above mentioned rather high pumping speeds results in the formation of foam in the propellant in the standard. This blending with air may be accompanied with an evaporation as a result of the relatively high vapour pressure of the propellant.
To oppose a kickback from the propellant and to be abreast of the foam formation the normal standard is provided with a tall funnel-shaped neck so that the filling nozzle may be kept at a distance above the level which indicates the determined correct charge of the standard, and the standard has to have a volume which corresponds to the lowest legal sales volume, e. g. five liters, and a comparatively broad sole to be able to stand solidly during the filling.
Two liquid indicating glasses, with markings for reading the liquid volume, are placed in diametrically opposite sides of the funnel-shaped neck. Hereby it is possible to calculate a mean value for the readings so that it is possible to compensate for a vertically abberant position of the neck or the longitudinal axis of the standard.
Substantially larger standards are also in existence, e. g. with a volume content of 20 liters.
A filled standard therefore may represent a considerable weight which may be a great disadvantage when it has to be carried from a pump to the filling pipe at the storage tank and when it has to be handled during the emptying.
To ensure uniform conditions during the emptying at several subsequent measurements it is, to counter measuring errors as a result of remnants of propellant left over from previous measurements, common practice to tip the standards and let the propellant flow from the top of the standard till the remnants are leaving the standard drop by drop at intervals of one second, which in practice is based on the time sense of the inspector in question with the resulting inaccuracy of measurement.
The propellant gives off vapours during the filling which partly are unhealthy to inhale and partly represent an element of danger because of their inflammability.
The above described method of control of propellant pumps by means of standards therefore represents a rather large manual task which furthermore is connected with danger of life and health.
To counter these disadvantages a calibration apparatus is known, f. inst. from Norway, of the kind mentioned in the introduction.
In this apparatus a two-wheeled trailer is employed which at front is provided with a coupling arrangement so that the trailer may be connected to and be drawn by a motor vehicle. Several standards of various sizes from the smallest to the largest prescribed size are placed on each side of the trailer. Each of the standards has at the bottom a draining opening which through a short, rigid and transparent hose and a manually operated valve is connected to a reception tank in the bottom of the trailer. The standards have a tall narrow neck which is provided with windows on two diametrically opposite sides, and which windows have engraved measurings lines. The tall narrow necks ensure in a commonly known way that even a small change in the volume of a liquid poured into the standard will result in a large change in the level of the liquid in the narrow neck. The neck of each of the standards is provided at the top with an open funnel which serves to direct liquid into the neck.
The standards are fixed to the trailer and as the surface at the petrol stations is slanting towards a drain with a rather large downward gradient to promote a quick collecting of spilled propellant, the standards may not right away be placed with their longitudinal axes in a vertical position which is a condition for the correct reading of the liquid level in relation to the reading lines of the windows. It will therefore be necessary, as when the traditional loose or free standards are used, to make readings of the two opposite windows or indicating glasses and calculate a mean value. This is a difficult and time-consuming process.
It is possible to supervise through the transparent hose after the manual opening of the draining valve that the propellant flows from the standard down into the collection tank, but it is not possible to ascertain when a uniform amount of liquid residue is left in the standards.
The open funnels involve a risk of spreading of vapours which implies dangers of fire and explosions and environmental hazards. Furthermore, the trailer has to be driven to the filling pipe of the subterranean tank so that the propellant may be emptied into the tank which implies unnecessary driving on the premises of the petrol station, as the filling pipe usually is situated far from the propellant pumps.